FM transmitter - theory, tools
FM-transmitter... we can see more and more devices with this label and with a decreasing price. Based on its name it’s easy to figure out what does such a device really do: it transmits data on shortwave. The question is what kind of data, as most of us FM means radio devices, but this time we’re talking about something different, so if you’d like to operate a pirate radio than go looking somewhere else.
This won't work
We can perceive FM transmitters as car handsfree sets. When sitting in our car many of us might have thought that it would be much better to listen songs from our MP3 players instead of dumb words flowing from the radio, but in the era of car CD players we don’t have many choices. The first is to buy a BMW, which has an iPod cradle… hooray. The second opportunity comes if our player has a line-in port, than we have a really simple task. Third case: the CD player has a USB port, but this might be problematic, as this is not compatible with all MP3 players, usually only with those that can function in USB Mass Storage mode. In the era of tapes everything was solved with a converter tape.
FM transmitters solve all our troubles in a very simple and logic way. Almost all cars have an FM tuner (radio), so we just have to transmit MP3 music from an MP3 player/phone/anything on a certain frequency and then set the radio to the same one and the miracle’s done.
All countries have an official authority that is responsible to specify who can transmit on which frequency. There are usually two frequency ranges on which transmission is allowed without a license. The first is the 26 960-27 410 kHz 40 band, except 26 995, 27 045, 27 095, 27 145 and 27 195 kHz frequencies. In these ranges only F3E or G3E (frequency- or phase-modulated) type CEPT PR 27 radio devices are allowed to function. The second range includes 446,0-446,1 MHz, in which short-range commercial radios (PMR 446) can operate. As we can see both are quite far from the 88-108 MHz range used by “normal” radios. Still, the use of FM transmitters is not illegal, but they are forced to have a capacity below 500 mW. As an interesting fact, in the UK transmitters cannot be used without a license.
That’s about that theory. Our current review is about E-TEN glofiish X650 Pocket PC, which is a PDA that theoretically has an FM transmitter. We are planning to write a review in the near future about accessory transmitters, that can be used with any device.
A cikk még nem ért véget, kérlek, lapozz!
